The present invention relates to shear pin assemblies and more specifically relates to such assemblies for connecting the hub of a driven member to a rock or drive shaft.
The idea of connecting the hub of a driven member to a drive member by means of a shear pin assembly including a pin designed to shear at a predetermined load so as to prevent the transfer of overloads between the drive and driven members is notoriously old. More specifically, it is known to provide the hub and shaft with diametrically positioned cross bores and to install the hub on the shaft by placing it over the latter with the cross bores in alignment and with a shear pin inserted in the cross bores and retained therein by some means.
The above-described known shear pin assembly is satisfactory when the shear strength requirement is such that a relatively soft pin can be used. However, it is not satisfactory when the shear strength requirement is such that a relatively hard pin must be used since when the pin of such an assembly begins to shear, it often is caused to "smear" the shear surface (shaft to hub interface in the vicinity of the pin) and deforms the edges of the cross bores at the interface such as to make the removal of the sheared pieces very difficult. Further, the irregular sheared surfaces cause an elongated pin piece which is not easily deformed by the hub so this pin piece in the shaft often wedges the hub on the shaft in a position wherein the cross bores are misaligned thus requiring heavy tools to bring the bores back into alignment to permit the removal of the pin piece. Additionally, it has been found that the pin piece in the shaft may score the inside of the hub of the driven member and after several "shears" the edge of the cross bore of the hub in the vicinity of the pin will be severely deteriorated and may make replacement of the driven member necessary.